Github user GJL commented on a diff in the pull request:
https://github.com/apache/flink/pull/5487#discussion_r169632755
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/jobmaster/RescalingBehaviour.java
---
@@ -0,0 +1,49 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.runtime.jobmaster;
+
+import org.apache.flink.runtime.jobgraph.JobVertex;
+import org.apache.flink.util.FlinkException;
+import org.apache.flink.util.function.BiConsumerWithException;
+
+/**
+ * Definition of the rescaling behaviour.
+ */
+public enum RescalingBehaviour implements
BiConsumerWithException<JobVertex, Integer, FlinkException> {
+ // rescaling is only executed if the operator can be set to the given
parallelism
+ STRICT {
+ @Override
+ public void acceptWithException(JobVertex jobVertex, Integer
newParallelism) throws FlinkException {
+ if (jobVertex.getMaxParallelism() < newParallelism) {
+ throw new FlinkException("Cannot rescale vertex
" + jobVertex.getName() +
+ " because its maximum parallelism " +
jobVertex.getMaxParallelism() +
+ " is smaller than the new parallelism "
+ newParallelism + '.');
+ } else {
+ jobVertex.setParallelism(newParallelism);
+ }
+ }
+ },
+ // the new parallelism will be the minimum of the given parallelism and
the maximum parallelism
+ RELAXED {
--- End diff --
Are you going to make this configurable in a follow up?